1. Field of the Invention
This invention relates to a magneto-optical eraser for erasing or initializing information which is recorded on a magneto-optical recording medium by utilizing a light beam and a magnetic field.
2. Description of the Related Art
FIG. 9 of the accompanying drawings shows a magneto-optical eraser disclosed in our co-assigned Japanese Patent Application No. 144389/1987. In FIG. 9, an electromagnet 4 is located at a position spaced a suitable distance from a parabolic surface 2a of a reflector 2 so that a magnetic pole 4a of the electromagnet 4 confronts the reflector 2. A single light source 3 is disposed inwardly of the parabolic surface 2a of the reflector 2. In this prior arrangement, a magneto-optical recording medium 1 is disposed close to the magnetic pole 4a of the electromagnet 4. The magneto-optical recording medium 1 is a medium for recording and reproducing information by utilizing a light beam and a magnetic field, and includes a magnetic layer such as of a TbFeCo film having the axis of easy magnetization in a direction perpendicular to the film surface. When light emitted from the light source 3 strikes on the magneto-optical recording medium 1, this recording medium is heated, and at the same time, a perpendicular magnetic field of over 5,000 Oe is given over the entire surface of the magneto-optical recording medium 1 due to the electromagnet 4.
By this prior magneto-optical eraser, information recorded on the magneto-optical recording medium is erased in the following manner.
Firstly, the electromagnet 4 is energized so as to apply a perpendicular magnetic field of over 5,000 Oe over the entire surface of the magneto-optical recording medium 1. Then, light emitted from the light source 3 is projected on the entire surface of the magneto-optical recording medium 1. This energization and projection causes the temperature of the recording film surface of the magneto-optical recording medium 1 to rise to over 180.degree. C. With this temperature rise, the coercive force of the magneto-optical recording medium 1 drops to less than 500 Oe, and the directions of magnetization of the information recording surface are all caused to be uniform in the direction of magnetic field given from the electromagnet 4. As a result, the information recorded on the magneto-optical recording medium 1 in pattern of magnetization is erased.
A common problem with this prior arrangement is that heat emitted from the single light source 3 is not enough to increase the temperature of the magneto-optical recording medium 1 uniformly over its entire surface.
In the case where the magneto-optical recording medium is in a double-face form shown in FIG. 10, the prior eraser is encounters with the following problem. As shown in FIG. 10, the double-face magneto-optical recording medium is composed of two transparent substrates 5, 6 of a resin such as polymetylmethacrylate (PMMA), polycarbonate (PC), etc., and a pair of magnetic layers 7, 8 formed a respective substrates 7, 8 so as to confront each other and which are attached to each other via an adhesive layer 9. When initializing this double-face magneto-optical recording medium or erasing information recorded thereon, magnetizations of the respective surfaces of the confronting magnetic layers 7, 8 must be in mutually opposite directions, as indicated by the arrows, to make codes of respective signal outputs during the reproduction of information equal. However, according to the conventional method, upon application of magnetic fields, magnetizations of the respective layer surfaces would be inconveniently in one and the same direction. Therefore the conventional method cannot be useful for erasing information recorded on a double-face magneto-optical recording medium.